<html>  
<head>  
    <meta charset="UTF-8">  
    <title>距离某个时间点倒计时</title>  
    <script type="text/javascript">  
        function countTime() {  
            //获取当前时间  
            var date = new Date();  
            var now = date.getTime();  
            //设置截止时间  
            var str="2021/3/3 00:00:00";
            var endDate = new Date(str); 
            var end = endDate.getTime();  
            
            //时间差  
            var leftTime = end-now; 
            //定义变量 d,h,m,s保存倒计时的时间  
            var d,h,m,s;  
            if (leftTime>=0) {  
                d = Math.floor(leftTime/1000/60/60/24);  
                h = Math.floor(leftTime/1000/60/60%24);  
                m = Math.floor(leftTime/1000/60%60);  
                s = Math.floor(leftTime/1000%60);                     
            }  
            //将倒计时赋值到div中  
            document.getElementById("_d").innerHTML = d+"天";  
            document.getElementById("_h").innerHTML = h+"时";  
            document.getElementById("_m").innerHTML = m+"分";  
            document.getElementById("_s").innerHTML = s+"秒";  
            //递归每秒调用countTime方法，显示动态时间效果  
            setTimeout(countTime,1000);  
  
        }  
    </script>  
</head >  
<body onload="countTime()">  
    <div>  
        <span id="_d">00</span>  
        <span id="_h">00</span>  
        <span id="_m">00</span>  
        <span id="_s">00</span>  
    </div>  
</body>  
</html>
